One of the few things to bring my interest (as well as the hummingbirds) away from the Witt Winter Garden at this time of year are the spider-like orange and pink flowers of Royal grevillea (Grevillea victoriae). Just across Arboretum Drive from the meadow of the Pacific Connections Gardens is the Australia garden. Much of the Australia garden is yet to be developed, but the existing entry garden is rich in interesting textures and unusual sights.
Grevillea is a genus of plant from the family Proteaceae. Species in the genus range in size from a few inches tall to over 100 feet. Most species are native to rain forests, but some originate in the more open lands of Australia and a few are hardy enough to grow and sometimes flourish in the Pacific Northwest. Due to their intolerance for cold, poor drainage and rich soils (Grevillea evolved in naturally phosphorus poor soils and are now intolerant of any fertilizer containing phosphorus) they are rarely grown locally, but for the garden with the proper conditions they reward with gusto.
The flowers of Grevillea are individually small but are grouped together in an inflorescence as are most proteaceous plants. The flowers are also petal-less, but the narrow calyx tube, which splits into four lobes to reveal long styles, is typically brightly colored. The range of colors for Grevillea flowers is great and the inner and outer surfaces of the calyx are often quite different, which can add a dramatic flair. The inflorescences of Grevillea can generally be grouped into one of two forms. The flowers are either arranged in a spiral pattern resulting in an inflorescence resembling a colorful super-spider, or they are arranged all in one plane looking more like a toothbrush. This has led to such common names as …. wait for it… “spider flower” and “toothbrush plant”.
Grevillea victoriae, which flowers most heavily in the winter is also regarded as the cold-hardiest of the genus, sometimes surviving down to approximately 0 degrees Fahrenheit which would give it a USDA zone 7a rating. This assumes that there isn’t too much water, or too much shade, or too much phosphorus or–I can personally add–too much deer pressure. Where it survives, it can grow rapidly to a 7 foot by 7 foot shrub. The leaves are a handsome grey-green, silver-backed, lanceolate 4 inches. The flower buds are formed in late summer and so decorate the plant for months before they finally open in winter for the hummingbirds to sip from. Grevillea victoriae is a Great Plant Pick.
Another species present in the Australian entry garden is Grevillea juniperina. Differing from the royal grevillea, the leaves of Grevillea juniperina are 8-22 mm long and only 1-2 mm wide, leading to the common name of “prickly grevillea”. Grevillea juniperina varies from a prostrate to an upright form, depending on the area of Australia from which it originates. The flower color also varies from a yellow-green to red. The flower form is of the spider type. Cold tolerances of near 0 degrees F have been reported.
The cultivar G. juniperina ‘Molonglo’, located in the Australian entry garden, is reported as a hybrid of an upright form with red flowers from the Canberra region mated with a prostrate form with yellow flowers from the Budawang Ranges of New South Wales. Correspondingly, the ‘Molonglo’ cultivar has apricot colored flowers and grows as a low spreading shrub to 3 feet high and 6 feet wide. Flowering time is nearly year round with a peak in spring.
Grevillea x gaudichaudii (my second favorite specific epithet of all) is another spectacular example of the genus. This hybrid is endemic to New South Wales. G. x gaudichaudii is a natural hybrid between G. acanthifolia and G. laurifolia both of which occur in Australia’s Blue Mountains.
The leaves of G. x gaudichaudii resemble classic lobed oak leaves in shape and common Photinia leaves in coloration as new growth comes out bright red which then ages to green. The red coloration returns a bit in cold weather. The plant itself is a low growing spreader, vigorously achieving 10-15 feet in width by only 8-10 inches in height. Though quite drought tolerant once established, a little light watering in summer can greatly accelerate its growth. The flowers are of the toothbrush type and a shocking deep pink, coming in somewhere between scarlet and electric fuchsia. Bloom time runs from early spring into autumn.
Grevillea ‘Neil Bell’ is another excellent hybrid Grevillea for gardens of the Pacific Northwest. This cultivar originated as a chance seedling in the garden of Neil Bell of Monmouth, Oregon. A large rounded shrub to 8 feet tall and wide, the leaves are oblanceolate to 3 inches. Leaf coloration is similar to G. victoriae. Flowers are of the spider type and are described as tomato-red. Bloom time seems to be year round, peaking in colder weather. ‘Neil Bell’ has been recorded as surviving 5 degrees F with no damage. All of which might suggest some Grevillea victoriae parentage.
Cultivation of Grevillea species is quite simple if all cultural requirements are met. Grevillea plants are extremely drought tolerant and require no irrigation beyond one (possibly three) years of planting. Light irrigation in the summer can increase growth rate and decrease flower bud aborting in hot periods. But regular irrigation, especially into fall, can increase winter mortality. As previously stated, any fertilizer containing phosphorus must be avoided. Enriching the soil with compost should be avoided as well. Light tip pruning of shrubs will help keep the plant dense and will increase flowering. Though some Grevillea will grow in a bit of shade, flowering will decrease significantly without the sun.
Location: Australia Garden of Pacific Connections in the Washington Park Arboretum
Origin: Primarily Australia. Also Indonesia, New Caledonia and Papua New Guinea
Habit: Grevillea species hardy in the Pacific Northwest range from sprawling ground covers to sturdy, upright shrubs to 15 feet tall.
Hardiness: There are several species that can do fine in our zone 8 temperatures, however poor siting in shade and wet soils can limit a plant’s ability to make it through the winter.